mocha developer - Aug 2007 - mocking singletons

How can I safely mock a singleton without the mocked method living on  
outside the scope of the test method?

I''ve run into this problem with mocking methods on globals (gasp!) in  
the past by doing something like

def mock_my_global
   original = $my_global
   $my_global.expects(:foo).returns(''bar'')
   yield
   $my_global = original
end

Is there something similar I can do for a singleton? Right now I have  
this:

def mock_my_singleton
   m = mock("my singleton")
   m.expects(:foo).returns(''bar'')
   MySingleton.expects(:instance).returns(m)
   yield
end

Thanks for your help.

-justin

list mods: I sent a previous message to the list but my membership  
was pending so my message is too. This message is more concise than  
my previous one so please do not approve it :)

On 21/08/07, Justin Perkins <justin at spiceworks.com>
wrote:
>
> How can I safely mock a singleton without the mocked method living on
> outside the scope of the test method?

This is one of the things Mocha takes care of for you in the context of a
test method.

I''ve run into this problem with mocking methods on globals (gasp!)
in
> the past by doing something like
>
> def mock_my_global
>    original = $my_global
>    $my_global.expects(:foo).returns(''bar'')
>    yield
>    $my_global = original
> end
>
> Is there something similar I can do for a singleton? Right now I have
> this:
>
> def mock_my_singleton
>    m = mock("my singleton")
>    m.expects(:foo).returns(''bar'')
>    MySingleton.expects(:instance).returns(m)
>    yield
> end

Do something like the following...

def test_me
  m = mock("my singleton")
  m.expects(:foo).returns(''bar'')
  MySingleton.stubs(:instance).returns(m)
  # Mocha modifies the MySingleton#instance method at this point.
  # From now until the end of the test it will return the mock.
  # At the end of the test it will be reverted to its original
implementation.
end

You don''t need to explicitly revert the method to its original
implementation - Mocha does it for you.

list mods: I sent a previous message to the list but my
membership
> was pending so my message is too. This message is more concise than
> my previous one so please do not approve it :)

No problems. Thanks for letting me know.

-- 
James.
http://blog.floehopper.org

On Mon, 2007-08-20 at 20:26 -0500, Justin Perkins wrote:
> How can I safely mock a singleton without the mocked method living on  
> outside the scope of the test method?
This is how I did it:
http://jonathanleighton.com/blog/testing-singleton-classes

> On Aug 21, 2007, at 3:45 AM, Jonathan Leighton wrote:
> This is how I did it:
> http://jonathanleighton.com/blog/testing-singleton-classes
Can I define a teardown method in the test_helper or would your  
solution require a per-test-case teardown method to reload the  
singleton?

-justin

On Aug 21, 2007, at 2:38 AM, James Mead wrote:
>
> This is one of the things Mocha takes care of for you in the  
> context of a
> test method.
That''s what I thought but I was getting weird behavior when I ran all  
the tests that led me to believe the mocked method was lingering around.
>   MySingleton.stubs(:instance).returns(m)
That was it. As soon as I used stubs instead of expects, everything  
works fine. I believe that when you use expects on a singleton, the  
mock lingers after the test is complete.

-justin

On Tue, 2007-08-21 at 12:28 -0500, Justin Perkins wrote:
> > On Aug 21, 2007, at 3:45 AM, Jonathan Leighton wrote:
> > This is how I did it:
> > http://jonathanleighton.com/blog/testing-singleton-classes
> 
> Can I define a teardown method in the test_helper or would your  
> solution require a per-test-case teardown method to reload the  
> singleton?
I''m not sure why you''d want to do that? You''d only
need to "reload" the
Singleton when you are testing it, not in every single test. Maybe I''ve
misunderstood something...

Jon

On 21/08/07, Justin Perkins <justin at spiceworks.com>
wrote:
>
>
> On Aug 21, 2007, at 2:38 AM, James Mead wrote:
> >
> > This is one of the things Mocha takes care of for you in the
> > context of a
> > test method.
>
> That''s what I thought but I was getting weird behavior when I ran
all
> the tests that led me to believe the mocked method was lingering around.
>
> >   MySingleton.stubs(:instance).returns(m)
>
> That was it. As soon as I used stubs instead of expects, everything
> works fine. I believe that when you use expects on a singleton, the
> mock lingers after the test is complete.


That sounds wrong. "expects" should work as well. You may have found a
bug.
If you get the chance can you try and distill the failing scenario down to
the smallest self-contained test you can and post it too the list.

Thanks.

-- 
James.
http://blog.floehopper.org

On Aug 22, 2007, at 3:29 AM, Jonathan Leighton wrote:
> I''m not sure why you''d want to do that? You''d
only need to "reload"
> the
> Singleton when you are testing it, not in every single test. Maybe  
> I''ve
> misunderstood something...
In every test where I was mocking my singleton I would have to add an  
additional teardown method, since I''m retrofitting existing code to  
mock the singleton this would require more work than I think is  
necessary.

Maybe I''m just misunderstanding the implementation?

-justin